Abnormal small coronary artery function may cause limited coronary flow responses to stress, resulting in anginal symptoms and ischemia in some patients with chest pain despite angiographically normal coronary arteries. To assess the exercise hemodynamic correlates of coronary flow abnormalities measured in the cardiac catheterization laboratory, 105 patients with microvascular angina (defined as an increase in coronary vascular resistance during pacing stress after ergonovine administration in the absence of significant epicardial constriction and associated with the provocation of the patients typical chest pain) and 27 patients without any coronary flow abnormality (normal) were analyzed. Of the 105 patients with microvascular angina, 75 had normal electrocardiographic responses to treadmill exercise testing, 22 had ischemic responses, and 8 had bundle branch block responses to exercise. Patients with ischemic-appearing electrocardiographic responses to exercise and patients with bundle branch block responses to exercise had a significantly higher prevalence of abnormalities in the left ventricular ejection fraction response to exercise by radionuclide angiography in contrast to more normal ejection fraction responses to exercise in patients without ischemic ECG responses to exercise. Although the microvascular constrictor response to ergonovine administered in the catheterization laboratory was no different among the 3 microvascular angina exercise groups, the administration of dipyridamole caused less coronary vasodilatation in those patients with ischemic- appearing or bundle branch block responses to exercise compared to those with normal electrocardiograms during exercise. Thus, the limited coronary flow response to dipyridamole may be closely related to the limited ejection fraction response to exercise and the abnormal electrocardiographic response during exercise, presumably reflecting reduced maximum coronary flow available to the myocardium during exercise stress.